docs: def show_plot(t_array, th_array):
      """ Display theta vs t plot. """
      th_mean = gv.mean(th_array)
      th_sdev = gv.sdev(th_array)
      thp = th_mean + th_sdev
      thm = th_mean - th_sdev
      plt.fill_between(t_array, thp, thm, color='0.8')
      plt.plot(t_array, th_mean, linewidth=0.5)
      plt.xlabel('$t$')
      plt.ylabel(r'$\theta(t)$')
      plt.savefig('pendulum.pdf', bbox_inches='tight')
      plt.show()